In the case of a heavy duty tire for example, generally, its tread profile shape (a) is formed into a single arc shape in a vulcanization die as schematically shown in FIG. 7.
In a regular internal pressure state in which such a tire is mounted on a regular rim and a regular internal pressure is charged into the tire, however, there is a tendency that a tread surface swells radially outward in a region Y separated from a tire equator by a distance which is 0.5 to 0.7 times a half of a ground-contact width of the tread. Therefore, a circumferential length difference between the swelling portion (b) and the tread ground-contact edge (e) becomes great, a slip is generated between the tread surface on the side of the tread ground-contact edge and a road surface, and uneven wear such as so-called unbalanced wear is prone to be generated.
Hence, in order to suppress the unbalanced wear, as disclosed in Japanese Patent Application Laid-open No. H7-164823, in a tread profile shape, it is proposed that a tread ground-contact edge portion (so-called tread shoulder portion) is formed of a flat arc having a great radius of curvature as compared with a tire equator portion (so-called tread center portion), and a ground-contact length in a ground-contact surface shape of the tread shoulder portion is elongated.
According to this technique, however, rubber gauge thickness in the tread shoulder portion is increased, and excessive increase in the radius of curvature brings about disadvantage because accumulated heat rises a temperature and a belt end is peeled off. From this point of view, there is a limit for increasing the radius of curvature and a suppressing effect of unbalanced wear can not sufficiently be exhibited.
The present inventor focused attention on a relation between the ground-contact force and the uneven wear and studied the relation. As a result, the inventor found that a correlation between the ground-contact force and wear energy was strong, and if the distribution of the ground-contact force was specified, it was possible to suppress the uneven wear including the unbalanced wear and to equalize the wear without excessively increasing the rubber gauge thickness.
That is, it is an object of the present invention to provide a heavy duty tire capable of suppressing the uneven wear including the unbalanced wear and equalizing the wear without excessively increasing the rubber gauge thickness.